In the past, a wide variety of portable shelters have been used to include tents and similar structures, inflatable structures, geodesic domes, and various types of prefabricated structures. Tents have the advantage of being quick to erect, while pre-fabricated structures have the advantage of being sturdier, more permanent, and more capable of withstanding weather. The ideal portable shelter would be free-standing and quick and easy to erect, yet sturdy and capable of withstanding windy and stormy weather. Portable shelters, at least those used by the military services, would preferably have one further characteristic: they would provide protection not only against the weather, but also optionally provide protection against chemical and biological agents and nuclear fallout. None of the known prior art devices disclose a portable shelter having these ideal characteristics.
U.S. Pat. No. 3,666,174 to Brylka at et discloses a blower apparatus for air supported structures. The Brylka device is a larger trailer which contains a blower and filters for a double walled air-supported structure. The Brylka device has the same disadvantages as all air-supported structures, that is, a blower must be operating and consuming power constantly to keep the shelter erect. In addition, the requirement for operating a gasoline engine or electric generator at all times reduces its usefulness for military units operating in forward areas in a combat situation.
Another double wall shelter is disclosed in U.S. Pat. No. 2,649,101 to Suits. This shelter is also a pressure supported structure in that it uses a negative pressure to create rigid arches to support the structure. It consists of a double-wall shelter that is inflated only to create the desired shape, then the space between the walls, which has a blanket of insulating material, is evacuated to compress the insulating material and create a rigid arch. The inflating air can then be turned off and the structure will support itself as long as the arches remain under sufficient negative pressure.
A third prior art patent, U.S. Pat. No. 3,660,951 to Cadwell, shows a double walled air-inflated shelter protecting against shock waves from nuclear explosion. A triple wall structure that has varying degrees of pressurization is used to reflect and offset the shock wave pressure. Obviously, the pressures discussed in this patent are orders of magnitude higher than the pressure used for protection of personnel from contaminants. Moreover, this is not a portable shelter of the type contemplated by the present invention.
Another prior art device is U.S. Pat. No. 3,006,352 to Hozak, which discloses and claims a Door Frame and Roll-up Door Mechanism for Air Locks. The Hozak device is an air supported structure which has a frame inside the cover of the structure. The frame supports the cover of the structure when the pressure in the structure drops below ambient pressure. This device is a relatively inefficient and low pressure structure which does not have and does not need or suggest many of the features and capabilities of the present invention, as will be shown below.
Still another prior art device is U.S. Pat. No. 2,910,994 to Joy. This patent discloses a very low pressure, air supported structure which has no frame or supports. As in the case of the Hozak patent mentioned above, the Joy patent is a portable shelter but otherwise bears little similarity to the present invention, which has a number of features and capabilities not found in the Joy device. The Joy device suffers from the known inefficiences and disadvantages of conventional air supported structures, as will be shown and discussed more fully below.
Yet another prior art patent is U.S. Pat. No. 1,326,011 issued by Great Britain to Andrews. This British patent has a frame which, at first glance, bears some similarity to the frame of the present invention but yet is quite different, as an examination of the Andrews structure will show. In Andrews, the framework is inside the cover as in Hozak, while the present invention has a support framework which is outside the cover, making the present invention much more useful as a portable, quickly erectable and strikable shelter. The Andrews patent is nt pressurized and is a much less sophisticated structure than the present invention. It does not need and does not show or suggest many of the advanced features of the present invention and needed by the present invention in order to provide a lightweight portable shelter which protects military personnel and others against chemical and biological agents and against nuclear fallout, as will be disclosed in detail below.
Therefore, it is a general object of this invention to provide a lightweight, sturdy, free-standing, quickly erectable and strikable all-purpose utility structure which also provides protection against chemical and biological agents and nuclear fallout.
It is another object of this invention to provide a lightweight portable shelter having a very lightweight cover made of chemical agent resistant material.
It is a further object of this invention to provide a lightweight, free-standing portable structure which is substantially air tight and with a filtered air pressure source for pressurizing the main chamber of the shelter to a pressure sufficient to prevent reverse air-flow of contaminated air into the structure but not high enough to deform the integral fabric floor of the shelter.